1. Field of the Invention
The present invention relates to a surveying instrument, and more specifically relates to a surveying instrument having a phase-difference detection type focus detecting device which employs a beam-splitting optical system as an element of an optical distance meter of the surveying instrument.
2. Description of the Related Art
A conventional surveying instrument such as a total station has a function to measure the distance between two points and also horizontal and vertical angles. Such a conventional surveying instrument generally measures the distance between two points with an electronic distance meter (EDM) incorporated in or attached to the surveying instrument. The electronic distance meter incorporates an optical distance meter which calculates the distance via the phase difference between projecting light and reflected light and via the initial phase of internal reference light, or via the time difference between the projecting light and the reflected light. The optical distance meter includes a light-transmitting optical system for transmitting a measuring light (projecting light) to the target (sighting object) via the objective lens of a sighting telescope (collimating telescope) provided as a component of the electronic distance meter, and a light-receiving optical system for receiving light (reflected light) reflected by the target.
Among conventional surveying instruments having such an electronic distance meter, a surveying instrument whose electronic distance meter employs a prism having a dichroic mirror (wavelength selection mirror) that serves as a beam-splitting optical system is known in the art. Such a prism having a dichroic mirror is hereinafter referred to as a xe2x80x9cdichroic prismxe2x80x9d. The dichroic mirror reflects light with specific wavelengths while allowing light with other wavelengths to pass through. The dichroic prism is disposed between the objective lens and the eyepiece of the sighting telescope so that the measuring light, which is emitted by a light emitting element, is reflected by the dichroic mirror of the dichroic prism to be projected toward the target (sighting object) via the objective lens of the sighting telescope. The light which is reflected by the target and passed through the objective lens is selectively reflected by the dichroic mirror to travel to a light-receiving element.
On the other hand, advancements have been made in the development of surveying instruments provided with a sighting telescope having an autofocus system, wherein phase-difference detection type autofocus system is widely used in the autofocus therefor. With this system, an in-focus state is detected based on the correlation between two images formed by two light bundles which are respectively passed through two different pupil areas upon passing through different portions of an objective lens of the sighting telescope to bring the sighting telescope into focus in accordance with the detected in-focus state.
An object of the present invention is to provide a surveying instrument having a phase-difference detection type focus detecting device which employs a beam-splitting optical system as an element of the optical distance meter of the surveying instrument, wherein both the optical distance meter and the phase-difference detection type focus detecting device can operate with a high precision.
To achieve the object mentioned above, according to an aspect of the present invention, a surveying instrument is provided, including a sighting telescope having an objective lens and an eyepiece for sighting an object; a beam-splitting optical system positioned between the objective lens and the eyepiece, and having a wavelength selection mirror which reflects light with specific wavelengths while allowing light having wavelengths other than the specific wavelengths to pass through the wavelength selection mirror, the wavelength selection mirror being inclined with respect to a plane perpendicular to an axis of the sighting telescope; an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light toward the object via the wavelength selection mirror, and a light-receiving optical system for receiving light reflected by the object via the wavelength selection mirror; and a phase-difference detection type focus detecting device which detects a focus state from a correlation between a pair of images respectively formed by two light bundles which are passed through two different pupil areas on the objective lens and the wavelength selection mirror. The two different pupil areas are positioned so that the two light bundles which are respectively passed through the two different pupil areas are incident on the wavelength selection mirror at the same incident angle.
Preferably, the wavelength selection mirror includes a dichroic mirror.
In an embodiment, the surveying instrument according further includes a Porro-prism erecting system positioned between the beam-splitting optical system and the eyepiece.
In an embodiment, the phase-difference detection type focus detecting device includes an AF sensor unit positioned adjacent to the Porro-prism erecting system so that the AF sensor unit receives light reflected by the Porro-prism erecting system.
In an embodiment, the sighting telescope includes a focus adjustment lens positioned between the beam-splitting optical system and the Porro-prism erecting system.
In an embodiment, the optical distance meter includes a light-emitting element which emits the measuring light; and a light-receiving element which receives the measuring light reflected by the object and received by the light-receiving optical system.
According to another aspect of the present invention, a surveying instrument is provided, including a sighting telescope having an objective lens and an eyepiece for sighting an object; a beam-splitting optical system positioned between the objective lens and the eyepiece, and having a wavelength selection mirror which reflects light with specific wavelengths while allowing light having wavelengths other than the specific wavelengths to pass through the wavelength selection mirror, the wavelength selection mirror being inclined to a plane perpendicular to an axis of the sighting telescope; an optical distance meter which includes a light-transmitting optical system for transmitting a measuring light toward the object via the wavelength selection mirror, and a light-receiving optical system for receiving light reflected by the object via the wavelength selection mirror; and a phase-difference detection type focus detecting device which detects a focus state from a correlation between a pair of images respectively formed by two light bundles which are respectively passed through two different pupil areas of the objective lens and the wavelength selection mirror. The two different pupil areas are positioned so that a plane which passes respective centers of the two different pupil areas extends substantially perpendicular to a plane which includes an axis of light incident upon the wavelength selection mirror and an axis of light reflected by the wavelength selection mirror.
Preferably, the wavelength selection mirror includes a dichroic mirror.
In an embodiment, the surveying instrument further includes a Porro-prism erecting system positioned between the beam-splitting optical system and the eyepiece.
In an embodiment, the phase-difference detection type focus detecting device includes an AF sensor unit positioned adjacent to the Porro-prism erecting system so that the AF sensor unit receives light reflected by the Porro-prism erecting system.
In an embodiment, the sighting telescope includes a focus adjustment lens positioned between the beam-splitting optical system and the Porro-prism erecting system.
In an embodiment, the optical distance meter includes a light-emitting element which emits the measuring light; and a light-receiving element which receives the measuring light reflected by the object and received by the light-receiving optical system.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-139850 (filed on May 12, 2000) which is expressly incorporated herein by reference in its entirety.